Color purity temperature compensation system for a color picture tube

ABSTRACT

In a color picture tube having an apertured beam selecting grill or mask through which one or more electron beams are made to land on predetermined color phosphors applied to the face plate of the tube, thermal expansion of the grill or mask is compensated for, so as to avoid mislanding of the beam or beams, by providing an auxiliary magnetic deflection means in back of the main magnetic deflection or scanning means and operative in dependence on the operation of the main deflection means to produce magnetic flux in opposition thereto and including a core having a magnetic permeability that decreases with increasing temperature so as to similarly decrease the magnetic flux opposing that of the main deflection means, whereby the effective center of deflection of the beam or beams is shifted rearwardly in response to increasing temperature.

United States Patent Inventor Yuzo Fuse Tokyo, Japan Appl. No. 888,340Filed Dec. 29, 1969 Patented Apr. 6, 1971 Assignee Sony CorporationTokyo, Japan Priority Dec. 28, 1968 Japan COLOR PURITY TEMPERATURECOMPENSATION SYSTEM FOR A COLOR PICTURE TUBE 6 Claims, 9 Drawing Figs.

US. Cl 313/75,

Int. Cl H01 j 29/70 Field of Search 313/75, 76,

[56] References Cited UNITED STATES PATENTS 3,408,520 10/1968 Lindeman313/75 3,524,093 8/1970 Burdick et a1. 313/75 Primary Examiner-G. HarrisAttorneys-Lewis I-I. Eslinger, Alvin Sinderbrand and Curtis,

Morris & Safford ABSTRACT: In a color picture tube having an aperturedbeam selecting grill or mask through which one or more electron beamsare made to land on predetermined color phosphors-applied to the faceplate of the tube, thermal expansion of the grill or mask is compensatedfor, so asto avoid mislanding of the beam or beams, by providing anauxiliary magnetic deflection means in back of the main magneticdeflection or scanning means and operative in dependence on theoperation of the main deflection means to produce magnetic flux inopposition thereto and including a core having a magnetic permeabilitythat decreases with increasing temperature so as to similarly decreasethe magnetic flux opposing that of the main deflection means, wherebythe effective center of deflection of the beam or beams is shiftedrearwardly in response to increasing temperature.

Patented April 5, 1971 3,573,525

2 Sheets-Sheet 1 ATTORNEY 2 Sheets-Sheet 2 FIG. 4.

l w 1 F Patented April 6, 1971 FIG. 5.

FIG.

YUZO FUSE ATTORNEY COLOR PURITY TEMPERATURE COMPENSATION SYSTEM FOR ACOLOR PICTURE TUBE This invention relates generally to color picturetubes, and more particularly is directed to compensating for themislanding of the electron beam or beams that may result fromtemperature variations in the tube.

A color picture tube generally includes an electron beam selectingdevice, such as, apertured mask, grill or grid, disposed within the tubeadjacent the screen of color phosphors applied to the face plate of thetube and by which each beam is made to land on a predetermined colorphosphor in dependence on the angle of incidence of the beam withrespect to the beam selecting device when passing through an aperture ofthe latter. During operation of the color picture tube, the impingementof the electron beam or beams on the beam selecting device increase thetemperature of the latter and thereby effects thermal expansion of thelatter. Such thermal expansion changes the positions or alignments ofthe apertures of the beam selecting device in relation to the respectivesets or arrays of color phosphors of the screen, and the change inalignment increases progressively from the center of the beam selectingdevice toward the periphery of the latter. The change in positions oralignement of the apertures relative to the respective sets or arrays ofcolor phosphors results in mislanding of the beams, that is, in theimpingement of the beams on other than the respective color phosphors ofthe screen, and this causes deterioration of the color purity of theresultant picture on'the screen.

In order to avoid the described mislanding of the beams resulting fromthermal expansion of the beam selecting device, it has been proposed toreduce the distance from the beam selecting device to the screen as thetemperature of the beam selecting device increases. However, mountingthe beam selecting device for temperature responsive movement relativeto the screen requires the use of complicated structures for supportingthe beam selecting device and such struc tures have reduced resistanceto shocks or impacts.

Another previously proposed arrangement for avoiding the describedmislanding of the beams resulting from variations in the temperaturewithin the tube, includes an auxiliary deflection coil mounted on theneck of the tube, for example, adjacent the main deflection yoke bywhich the beam or beams are horizontally and vertically deflected so asto scan the screen, and a circuit by which a deflection current is madeto flow through the auxiliary deflection coil and is varied in responseto changes in the temperature of the beam selecting device. Suchvariation of the deflection current is selected so that the magneticfield produced by the auxiliary deflection coil serves to shift theeffective center of beam deflection in response to temperature changesand thereby maintains proper landing of the beams on the respective.color phosphors. However, such proposed arrangement does not providesufficient compensation for fully and reliably avoiding the describedmislanding, and the circuit required for varying deflection current inresponse to changes of temperature is complex and costly. Further, theproposed compensating arrangement adversely affects the linearitycharacteristic of the beam deflection die to the additional circuitelements required to provide the variable deflection current.

Accordingly, it is an object of this invention to provide a relativelysimple and reliable arrangement by which the effective center of beamdeflection in a color picture tube is shifted in response to temperaturevariations in the tube so as to effectively compensate for themislanding of the beam or beams that would otherwise result from thethermal expansion or distortion of the beam selecting device.

Another object is to provide a compensating arrangement, as aforesaid,which is operable by the current supplied to the main deflection yoke ofthe tube for effecting the horizontal, or the horizontal and verticaldeflections of the beam or beams, without adversely affecting thelinearity characteristic of such deflections.

In accordance with an aspect of this invention, a color picture tube isprovided with an auxiliary magnetic deflections means disposed in backof the main deflection yoke and being operative in dependence on theoperation of the main deflection yoke to produce magnetic flux inopposition to the magnetic flux provided by the latter, with suchauxiliary magnetic deflection means including a core having apermeability that decreases with increasing temperature so as tosimilarly decrease the magnetic flux acting in opposition to themagnetic flux produced by the main deflection yoke, whereby theeffective center of deflection of the beam or beams by the combinedeffects of the main deflection yoke and the auxiliary deflection meansis shifted rearwardly in accordance with increasing temperature tocompensate for thermal expansion of the beam selecting device.

More particularly, in a compensating arrangement according to thisinvention, the auxiliary magnetic deflection means includes a coil orcoils wound on the core of varying permeability and connected with thecorresponding coil or coils of the main deflection yoke so as to receivedeflecting currents flowing through the latter and thereby produce themagnetic flux in opposition to that of the main deflection yoke.

The above, and other objects, features and advantages of this invention,will be apparent in the following detailed description of illustrativeembodiments thereof which is to be read in connection with theaccompanying drawings, wherein:

FIG. 1A is a schematic, axial sectional view of a color picture tube towhich reference will be made in explaining the mislanding of an electronbeam that may result from thermal changes within the tube;

FIG. 1B is an enlarged detail view of a portion of the structure shownin FIG. 1A, and to which particular reference will be made in explainingthe compensation effected according to this invention;

FIG. 2 is a schematic elevational view of a color picture tube embodyingthis invention and as viewed from the top thereof;

FIG. 3 is a front elevational view of an auxiliary deflection deviceprovided on the tube of FIG. 2 in accordance with this invention;

FIG. 4 is a graph showing the variation of permeability with temperatureof a core included in the auxiliary deflection device of FIG. 3;

FIG. 5 is a schematic wiring diagram illustrating the manner in whichthe coil of the auxiliary deflection device of FIG. 3 is connected witha coil of the main deflection yoke of the color picture tube;

Fig. 6 is a schematic view illustrating the magnetic flux produced bythe auxiliary deflection device of FIG. 3 at an elevated temperature;

FIG. 7 is a view similar to that of FIG. 6, but showing the fluxdistribution at a low temperature; and

FIG. 8 is a view similar to that of FIG. 3, but illustrating anotherembodiment of this invention.

Referring to the drawings in detail and initially to FIG. 1A thereof, itwill be seen that a color picture tube 1, as there illustrated, has aphosphor screen 2 formed on the inner surface of its face plate and anapertured beam selecting device 3, for example, in the form of a shadowmask or aperture grill or grid suitably supported within the the tubeand spaced rearwardly from the phosphor screen 2. As is well known andparticularly shown on FIG. 1B, the phosphor screen 2 is made up of setsor arrays of primary color phosphors, as indicated at R, G and B, andthe purpose of the beam selecting device 3 is to determine which of thecolor phosphors a particular electron beam lands upon in dependence onthe angle of incidence of the beam with respect to device 3 at anaperture 4 of the latter through which the beam passes prior toimpinging against the corresponding set or array of color phosphors. Itwill be understood that the beam selecting device 3 is heated by theimpingement of the electron beam or beams thereon during scanning of thescreen, and such heating of the beam selecting device causes its thermalexpansion, for example, from the conditions shown in full lines of FIGS.1A and 18 to the condition shown in broken lines at 3, where the beamselecting device is spaced rearwardly from its normal or actual positionmerely for convenience of illustration. It will be seen that the thermalexpansion of the device 3 to the condition indicated at 3' results inthe displacement of the apertures 4 away from the central axis x-x ofthe tube, and that the extent of such displacement of the aperturesincreases progressively towards the periphery of the screen 2 and thebeam selecting device. Thus, for example, with respect to the aperture 4a, the heating of the beam selecting device 3 will effect thedisplacement of such aperture away from the tube axis to the positionindicated at 4'11.

Assuming that an electron beam B is deflected about the effective center0, as by the usual main deflection yoke 6 provided on the color picturetube 1, so as to follow the path 5 through the aperture 40 of beamselecting device 3 and to land on the corresponding color phosphor G, ofthe array or set A when the beam selecting device 3 is at a relativelylow temperature, it will be apparent that, in response to heating andthe resulting thermal expansion of the beam selecting device, theelectron beam B will be in the position 5 when it passes through thedisplaced aperture 4'a and thus will no longer land on the correspondingcolor phosphor G, but rather will misland on the color phosphor R withresulting deterioration of the color purity of the picture.

However, if the effective center of deflection of the beam B is shiftedfrom the position on FIG. 1A in the rearward direction, that is, awayfrom the screen 2 or beam selecting device 3, for example, to theposition 0', the beam, when deflected to the position will pass throughaperture 4'1 of the thermally expanded beam selecting device 3' andagain land on the corresponding color phosphor G,, of the respectivephosphor set A, whereby to compensate for the thermal expansion of thebeam expansion of the beam selecting device and to avoid deteriorationof the color purity of the picture. Thus, mislanding of the electronbeam or beams can be avoided by suitably shifting the effective centerof deflection of each electron beam in response to temperature changeswithin the tube.

In accordance with the present invention, particularly as illustrated onFIG. 2, a color picture tube 1 having an electron gun 7 directing threebeams B B and B toward color screen 2 and causing such beams to convergeat a common aperture of the beam selecting device 3 is provided with anauxiliary magnetic deflection device 8 in addition to the usual maindeflection yoke 6 by which the three beams are deflected horizontallyand vertically so as to scan the screen. When the color phosphors ofscreen 2 are applied in the form of vertical stripes and beam selectingdevice 3 is constituted by an aperture grill having vertical slitstherein corresponding to the respective sets or arrays of color phosphorstripes, then the auxiliary deflection device 8 according to thisinvention need provide mislanding compensation only with respect to thehorizontal deflections of the beams.

As shown on FIG. 2, the auxiliary deflection device 8 is mounted on theneck of tube I at the side of main deflection yoke 6 remote from screen2, that is, in back of yoke 6, and comprises an annular magnetic core 10and a coil 11 made up of two coil portions Ila and 11b (FIG. 3) whichare electrically connected, for example, in series, and wound on opposedside portions of core 10 so that, in response to a current flow throughcoil 11, there is produced a magnetic flux, as indicated at F on FIG. 6,to effect horizontal deflection of the beams B B and B,,. As indicatedon FIG. 5, the coil 11 of device 8 is connected, for example, in series,with the horizontal deflection coil 6H of the main deflection yoke 6 sothat, when a horizontal deflection current is supplied to coil 6H by wayof terminals 9a and 9b to effect horizontal scanning deflection of thebeams, such current will also flow in coil II to produce the magneticflux F in opposition to the magnetic flux produced by the currentflowing in the coil 6H.

III

In accordance with this invention, the core 10 of auxiliary deflectiondevice 8 is formed of a magnetic material having a permeability thatvaries in response to temperature changes, and more particularly havinga permeability that decreased with increasing temperature. Such magneticmaterial having a permeability varying in accordance with temperaturemay be an alloy composed of 70 percent iron and 30 percent nickel havingthe temperature-permeability characteristic illustrated on FIG. 4. Thus,when core 10 is substantially at room temperature, it has a relativelyhigh permeability 11., and, as the core 10 is progressively heated, itspermeability is progressively reduced until it is lowered to the valuet, at the critical temperature T which value of permeability correspondsto that of a vacuum.

Although the auxiliary deflection device 8 is mounted on the neck oftube 1, for example, adjacent to the main deflection yoke 6, as shown,it has been found that, during operation of the color picture tube, therise in temperature of the core 10 will be a function of, or correspondto the rise of temperature of the beam selecting device 3.

When the operation of tube I is initiated, that is, when core 10 isrelatively cool and has a high permeability, the magnetic flux Fproduced by coil 11 in response to the horizontal deflection currentflowing therethrough will be substantially concentrated within the neckof tube 1 (FIG. 7) to oppose the magnetic flux resulting from the flowof the same current through main coil 6H. Since device 8 is disposed inback of yoke 6, that is, at the side of yoke 6 remote from screen 2, themagnetic flux F of coil 11 will more or less counteract the magneticflux of coil 6H at the back end portion of yoke 6 in that the effectivecenter of deflection of the beams will be at a relatively forwardposition, for example, at the position 0 on FIG. 1A, whereby properlanding of the beams on the respective color phosphors will be obtainedwith the beam selecting device at a relatively low temperature. As theoperation of the color picture tube continues with consequent heatingand thermal expansion of beam selecting device 3 and correspondingheating of core 10, the permeability of the core is reduced to diminishthe concentration of the magnetic flux F which acts within the tube neckon the beams B B and B (FIG. 6). Thus, as the permeability of core 10 isprogressively decreased, the efi'ect of magnetic flux F in opposition tothe magnetic flux produced by coil 6H at the back end portion of yoke 6is also progressively decreased so that the effective center ofdeflection of the beams is moved rearwardly, for example, to theposition 0 on FIG. 1A. Finally, at the temperature T,,, the core 10 hasits permeability reduced to the value t, so that the core is thenwithout any magnetic effect and the flux of coil 11 is diffused.

It will be understood that the number of windings or turns in the coil11 is relatively small as compared with that of coil 6H, and is selectedso as to be sufficient only to provide, in association with the core 10,the displacement of the center of deflection of the beams for achievingthe described compensation. Although the inductance of the auxiliarydeflection device 8 may vary with changes in temperature, the number ofwindings of coil 11 is sufficiently small, as compared with the numberof windings in coil 6H, so that the effect of the varied inductance onthe horizontal deflection current can be neglected. Thus, in accordancewith the present invention it is not intended to seek to compensate formislanding by varying the deflection current itself, for example, byvarying the inductance of the circuit for the deflection current inresponse to temperature changes.

When the color picture tube has a shadow mask as its beam selectingdevice and the color phosphors are applied in sets or arrays of dots,then it is necessary to compensate for temperature induced mislanding inthe vertical as well as the horizontal directions. As shown on FIG. 8,when the beam selecting device 3 is a shadow mask and the screen 2 hasits color phosphors in the form of dots, the auxiliary deflection deviceIOHHK mu e...

111;, a second coil 12 wound in portions 12a and 12b on the top andbottom portions of core 10.

The coil portions 120 and 12b are connected to each other, as shown, andalso connected with the vertical deflection coil (not shown) of yoke 6so that, when the vertical deflection current flows in the verticaldeflection coil of yoke 6, such current also flows through coil 12 tocause the latter to produce a magnetic flux which is more or lessconcentrated to act on the beams in dependence or the permeability ofcore 10. Such flux produced by coil 12 acts similarly to the describedaction of the flux of coil 11 to achieve the desired compensation withrespect to the vertical deflection of the beams.

Although illustrative embodiments of the invention have been describedin detail herein with reference to the drawings, it is to be understoodthat the invention is not limited to those precise embodiments, and thatvarious changes and modifications may be effected therein withoutdeparting from the scope or spirit of the invention.

lclaim:

1. In a color picture tube including an envelope having a faceplate, ascreen of phosphors coated on said faceplate for emitting light ofrespective predetermined colors, an electron gun device for generatingat least one electron beam directed toward said faceplate, aperturedbeam selecting means disposed adjacent said faceplate to land said beamon selected phosphors of said screen in accordance with the angle ofincidence of said beam to said beam selecting means at the apertures ofthe latter, and main magnetic deflection means for deflecting said beamso as to cause scanning of said screen; the improvement comprisingauxiliary magnetic deflection means disposed at the side of said maindeflection means remote from said screen and being operative independence on the operation of said main magnetic deflection means toproduce magnetic flux in opposition thereto, said auxiliary magneticdeflection means including a core having a permeability that decreaseswith increasing temperature so as to similarly decrease said magneticflux in opposition to the magnetic flux produced by said main magneticdeflection means, whereby the effective center of deflection of saidbeam by the combined effects of said main and auxiliary magneticdeflection means is shifted in the direction away from said screen inaccordance with increasing temperature to compensate for thermalexpansion of said beam selecting means.

2. A color picture tube according to claim 1, in which said maindeflection means include coil mans to produce magnetic flux fordeflecting said beam upon a current flow therethrough, and saidauxiliary deflection means includes additional coil means wound on saidcore and electrically connected with said coil means of the maindeflection means to produce said magnetic flux in opposition to the fluxof said main deflection means in response to said current flow.

3. A color picture tube according to claim 2, in which said auxiliarydeflection means is disposed adjacent to said main deflection means.

4. A color picture tube according to claim 2, in which said coil meansof the main deflection means includes horizontal and vertical deflectioncoils to produce magnetic flux for deflecting said beam horizontally andvertically, respectively, said additional coil means is connectedelectrically with said horizontal deflection coil and is arranged todeflect said beam horizontally in opposition to the horizontaldeflection of said beam resulting from said current flow through saidhorizontal coil, said phosphors are in the form of vertical stripes onsaid faceplate, and said apertures of the beam selecting means are inthe fonn of vertical slits.

5. A color picture tube according to claim 2, in which said coil meansof the main deflection means includes main horizontal and verticaldeflection coils to produce magnetic flux for deflecting said beamhorizontally and vertically, respectively, and said additional coilmeans includes auxiliary horizontal and vertical deflection coilselectrically connected with said main horizontal and vertical deflectioncoils, res ectrvely, and being arranged to deflect sard beam horizonally and vertically in opposition to the horizontal and verticaldeflections of the beam resulting from current flows through said mainhorizontal and vertical deflection coils, respectively. 6. A colorpicture tube according to claim 2, in which said core is in the form ofa ring disposed on the neck of said tube.

1. In a color picture tube including an envelope having a faceplate, ascreen of phosphors coated on said faceplate for emitting light ofrespective predetermined colors, an electron gun device for generatingat least one electron beam directed toward said faceplate, aperturedbeam selecting means disposed adjacent said faceplate to land said beamon selected phosphors of said screen in accordance with the angle ofincidence of said beam to said beam selecting means at the apertures ofthe latter, and main magnetic deflection means for deflecting said bEamso as to cause scanning of said screen; the improvement comprisingauxiliary magnetic deflection means disposed at the side of said maindeflection means remote from said screen and being operative independence on the operation of said main magnetic deflection means toproduce magnetic flux in opposition thereto, said auxiliary magneticdeflection means including a core having a permeability that decreaseswith increasing temperature so as to similarly decrease said magneticflux in opposition to the magnetic flux produced by said main magneticdeflection means, whereby the effective center of deflection of saidbeam by the combined effects of said main and auxiliary magneticdeflection means is shifted in the direction away from said screen inaccordance with increasing temperature to compensate for thermalexpansion of said beam selecting means.
 2. A color picture tubeaccording to claim 1, in which said main deflection means include coilmans to produce magnetic flux for deflecting said beam upon a currentflow therethrough, and said auxiliary deflection means includesadditional coil means wound on said core and electrically connected withsaid coil means of the main deflection means to produce said magneticflux in opposition to the flux of said main deflection means in responseto said current flow.
 3. A color picture tube according to claim 2, inwhich said auxiliary deflection means is disposed adjacent to said maindeflection means.
 4. A color picture tube according to claim 2, in whichsaid coil means of the main deflection means includes horizontal andvertical deflection coils to produce magnetic flux for deflecting saidbeam horizontally and vertically, respectively, said additional coilmeans is connected electrically with said horizontal deflection coil andis arranged to deflect said beam horizontally in opposition to thehorizontal deflection of said beam resulting from said current flowthrough said horizontal coil, said phosphors are in the form of verticalstripes on said faceplate, and said apertures of the beam selectingmeans are in the form of vertical slits.
 5. A color picture tubeaccording to claim 2, in which said coil means of the main deflectionmeans includes main horizontal and vertical deflection coils to producemagnetic flux for deflecting said beam horizontally and vertically,respectively, and said additional coil means includes auxiliaryhorizontal and vertical deflection coils electrically connected withsaid main horizontal and vertical deflection coils, respectively, andbeing arranged to deflect said beam horizontally and vertically inopposition to the horizontal and vertical deflections of the beamresulting from current flows through said main horizontal and verticaldeflection coils, respectively.
 6. A color picture tube according toclaim 2, in which said core is in the form of a ring disposed on theneck of said tube.